This invention relates to a fastening assembly for the fastening of systems in an aircraft.
The structure of the fuselage of an aircraft usually is made up of frames extending in transverse planes, stringers extending more or less along a longitudinal direction of the aircraft outside the frames, and a skin that covers the said stringers and is fastened thereto. The skin also is fastened to the frames, through connecting pieces known under the name of “clip” or “stabilizer.”
In the cabin in particular, the interior faces of the fuselage are covered successively by insulation blankets, producing a thermal and sound insulation of the cabin, and by covering panels the interior face of which remains visible from the cabin and thus forms a finish face. Between two successive frames of the fuselage, the skin of the said fuselage is covered by insulation blankets called field blankets, (called “field blankets” in English). Each frame of the fuselage is further covered by a blanket called frame blanket (called “frame blanket” in English). An overlap zone may be provided between consecutive frame and field blankets.
Between the insulation blankets and the covering panels, systems are arranged (equipment items, electrical cables, hydraulic and pneumatic systems . . . ).
These systems usually are fastened to the structure of the fuselage by localized fastening devices traversing the insulation blankets covering the said structure. Thus, for example, the electrical cables are fastened to the frames of the fuselage with the aid of localized fastening devices comprising a rod which traverses the frame and the blanket or blankets which cover it. These localized fastening devices also comprise washers for locking the rod on both sides of the frame, and a lug into which there engages a quick-clamping collar receiving one or more wirings. As regards the pipes provided for the circulation of conditioned air, they usually are fastened to the stringers, with the aid of localized fastening devices comprising a clamping collar borne by a support fastened to a stringer by screws; these screws traverse the stringer and field blanket covering the latter.
For fastening of the systems, it therefore is necessary to make holes in the structure of the fuselage as well as in the insulation blankets.
The holes made in the structure weaken the latter and therefore make it necessary to provide thickened zones or other structural reinforcements close to them. These holes therefore complicate the design of the fuselage.
Holes made in the insulation blankets degrade the insulation performances of the latter, creating as many thermal and acoustic bridges. They also reduce their watertightness (as it happens, the insulation blankets also have the function of draining, to the trough bottom of the fuselage, the water of condensation appearing on the skin of the aircraft). Moreover, the making of these holes considerably complicates the manufacture of the blankets and weights down the cost prices thereof. Thus for example, at each hole made on a blanket edge for fastening electrical cables to the frames (and for fastening the blankets themselves to the said frames), the layer of glass wool of the blanket must be replaced by a foam rubber disk, which facilitates making of the hole and reinforces the blanket around the said hole so as to prevent the blanket from tearing.
Moreover, in the event of belated modification (when the aircraft is in assembly phase for example) of the structure of the fuselage or of a system, it is necessary to make one or more additional holes in the blanket concerned and/or in the structural element concerned.
The making of an additional hole in a blanket is a particularly long and tedious process. To this end, it is advisable, in fact, to bond an adhesive strip on each face of the blanket at the location of the hole, cut out a disk in the blanket at the location of the hole with the aid of a first specific cutting tool, remove the blanket disk cut out in this manner and replace it with a foam rubber disk, again bond an adhesive strip on each face of the blanket so as to cover and hold the foam rubber disk, pierce the blanket in the center of the foam rubber disk with the aid of a second specific cutting tool so as to form the hole. When an additional hole is made in a blanket, it furthermore is necessary to fill up the henceforth unused hole in the blanket.
The belated making of holes in a structural element also poses a problem. These holes weaken the structure and, because they are not provided for during design of the fuselage, often make it necessary to add structural reinforcements. Moreover, when the structure is of a composite material, the making of a hole requires the use of a specific tool, generates chips that are harmful—and therefore hazardous for the operator in charge of making the hole—and may cause delaminations of the composite material around the hole. These problems are more difficult to control when making of the hole is not provided for at the outset, and is not done at the manufacturing site of the structure.
For all the reasons indicated above, it is desirable to limit the number of holes made in the structure and in the blankets for fastening the systems.